A problem in the prior art has been that state-of-the-art harmony processors are somewhat restricted in use due to the fact that such real-time processors are controlled by keyboards or other monophonic control signal establishing provisions. A keyboard is well-suited for the purpose as keyboards by nature establishes such control signals typically as a so-called MIDI (Musical Instrument Digital Interface) signal, which may be transmitted by simple measures to other relevant devices such as other keyboards, modules, audio processors, sequencers, etc. The control signals provided are typically polyphonic and regarded as well-suited for the purpose of controlling e.g. a harmony processor in real-time.
A challenge in this connection has been that instruments, in particular polyphonic instruments such as guitars, establishes the desired tones mechanically and that such tones are therefore represented as an audio signal without the use of tone generators, etc. as in systems where keyboards are applied. Basically, such an “analog” musical instrument provides a resulting audio signal comprising no control information regarding choice of tones, volume, sustain, pitch, etc. Such information may, however, be derived e.g. in batch processing as the information must be derived by means of significant processing power.
Moreover, a further problem is that a real-time harmony processing by nature requires a voice input as an input signal simultaneous with the above-mentioned analysis in order to provide the voice material upon which a the harmony processing may be based.